CLASSIFICATION AND ORIGIN OF INSECTS 1407 



The sawflies are so called because they possess at 

 the end of the body a curious organ, corresponding to 

 the sting of a wasp, but which is in the form of a 

 fine-toothed saw. With this instrument the female 

 sawfly cuts a slit in the stem or leaf of a plant, into 

 which she introduces her egg. The larva much re- 

 sembles a caterpillar, both in form and habits. To 

 this group belongs the nigger, or black caterpillar 

 of the turnip, which is often in sufficient numbers to 

 do much mischief. Some species make galls, but the 

 greater number of galls are formed by insects of an- 

 other family, the Cynipidae. 



In the Cynipidae the female is provided with an 

 organ corresponding to the saw of the sawfly, but 

 resembling a needle. With this she stings or punc- 

 tures the surface of leaves, buds, stalks, or even roots 

 of various plants. In the wound thus produced she 

 lays one or more eggs. The effects of this proceeding, 

 and particularly of the irritating fluid which she 

 injects into the wound, is to produce a tumor or 

 gall, within which the egg hatches, and on which 

 the larva, a thick fleshy grub, feeds. In some species 

 each gall contains a single larva; in others, many 

 live together. 



The oak supports several kinds of gallflies: one 

 produces the well-known oak-apple, one a small 

 swelling on the leaf resembling a currant, another a 

 gall somewhat like an acorn, another attacks the 

 root; the species making the bullet-like galls, which 

 are now so common, has only existed for a few years 

 in England; the beautiful little spangles so common 

 in autumn on the under side of oak leaves are the 



